Re: need a bit of early boot help

Den 2025-11-27 kl. 18:01, skrev Dave McGuire:
> On 11/11/25 05:52, Johnny Billquist wrote:
>>>> And VMS also hangs after printing a banner... Which would suggest 
>>>> that there is something funny either with the printing on the 
>>>> console, but which is interrupt related, or something else is 
>>>> getting the machine stuck at an elevated privilege mode, preventing 
>>>> interrupts from being processed.
>>>>
>>>> I would actually probably suspect something else isn't completing, 
>>>> and the processor is stuck at some elevated prio. The console is 
>>>> probably working just fine, including when interrupt driven. But 
>>>> something else is not.
>>>>
>>>> I assume we're talking about a real machine here. So it has actual 
>>>> Unibus. Simple suggestions would be to remove everything not 
>>>> absolutely required to get the machine running, and really make 
>>>> sure you have bus grants in all Unibus slots not having a card in 
>>>> it. Also, make sure the NPR jumper is in place. This one can be a 
>>>> bit tricky, since it's actually a wire on the back side of the 
>>>> backplane, which might have been cut. There a double height bus 
>>>> grant cards that also covers the NPR signal, but the small square 
>>>> ones do not.
>>>>
>>>> And if the Unibus isn't properly configured, you can probably get 
>>>> things hung/stuck for some time.
>>> It's a 780, Unibus is not involved here at all :-)
>>> The PDP11 is connected directly to the backplane (SBI).
>>
>> Well. Yes an no.
>> The PDP11, which is the FE, don't have any Unibus at all. And the 
>> machine boots, and there is terminal I/O to the console, and the 
>> system starts running.
>>
>> But something happens somewhere along the way. And the *VAX* have a 
>> Unibus, and it will be probed somewhere along the way, and that is 
>> where I wonder what might be going on.
>>
>> I don't think there are any problems at all with the PDP11 FE.
>
>    [I had sent this last night, but it didn't make it to the list, 
> presumably due to the attached photo...sending without the photo this 
> time]
>
>    Summary: IT RUNS!
>
>     The problem was in the CIB board, a failed 74S74 flip flop in 
> interrupt handling.
>
>    We'll post pics and such soon.
>
>    Thanks everyone for the guidance.  We'll try booting VMS on it 
> later tonight, temporarily from the VAX-11/750's system disk.  If all 
> goes well there, we'll set up permanent system disks for it for VMS, 
> NetBSD, and possibly Ultrix-32.
>
>    Incidentally, this is the same '780 that Gunther Schadow had quite 
> a saga with on this very mailing list, back in 2002.  To my knowledge 
> he never did get it running.  We fixed a number of hardware problems 
> in this machine, so it's no wonder he'd had such a tough time with 
> it.  It was many months of work, off and on, over several years for us 
> here at LSSM.
Cool! Real hardware fix!

How did you manage to find the failing chip?  I.e. the error isolation 
process? :-)

-- Ragge